I'm the dad of a Class of 2019 pitcher. I'm not a baseball/pitching expert, so my comments only relate to my son's experience of being in your shoes.
I have noticed for the last year or so that my son had some mechanical problems with his pitching motion, just by comparing his form to other really good pitchers in our league, as well as pro pitchers who are known as having great mechanics. I was concerned about his performance, velo, etc., but my main concern was whether any problems with his mechanics were making him more prone to injury. We worked with a couple of pitching coaches and tried some remote training via video and Skype without much improvement. We finally decided to do the Elite Pitcher's Boot Camp at the Texas Baseball Ranch. They're big on spotting mechanical flaws (they call them "disconnections") that they think hinder performance and/or increase injury risks. They work with a number of tools, but one of the main ones is a connection ball: https://www.oatesspecialties.com/connection-ball-12. You do various drills that involve throwing a baseball into a net while holding the connection ball in different ways, based on the flaw you're trying to fix. After a month of doing the connection ball drills for 15 minutes about 5 times per week, my son's arm action has improved DRAMATICALLY. His control/command has also improved. Obviously we're big believers in the TBR training, so I'd highly recommend that, but you can also find a number of connection ball drills online for free (the connection balls themselves are cheap). I'm sure there are many other options for improving your mechanics; this is just my two cents based on my son's experience. Good luck!